Over the history of development of switched mode power supply systems (SMPS) or resonant converters, the rectifier circuit side of the converter has increased in complexity.
In traditional resonant SMPS, the rectifier circuit portion of the SMPS included conventional semiconductor diode rectification components, which rectified the voltage signal produced by the resonant tank portion of the converter. In order to control the output voltage of the converter, the frequency at which the resonant tank was switched was varied.
In order to make this form of converter more efficient, synchronous rectification was introduced. Synchronous rectification involves placing semiconductor switches in parallel with (or replacing) the conventional rectifier diodes. Typically the semiconductor switches are MOSFET (Metal Oxide Semiconductor Field Effect) devices. However the MOSFET devices could be replaced by IGBT (Insulated Gate Bipolar Transistor) devices or a number of alternate devices.
For example, a typical SR circuit is shown in FIG. 1. A resonant tank 101 consisting of a capacitive element and an inductive element in series receives power from a power source 103 via a switch circuit 105. A shunt inductor 106 is placed in parallel across the primary winding of an isolation transformer 107. The output of the isolation transformer 107 includes synchronous rectification switching devices 109, which provide output power to a load 113 via a smoothing capacitor 111.
This type of LLC circuit has the ability to provide output voltage control by operating in either the buck or boost regions. Further, the recent shift in industry standard practice to employ this type of output synchronous rectification has resulted in the capability of providing bidirectional power conversion. It has been discovered that the conventional LLC series resonant circuit has an asymmetric transfer function, where the input to output transfer function (i.e. forward transfer function) is different to the output to input transfer function (i.e. reverse transfer function).
However, it has been found that the reverse transfer function does not facilitate practical reverse power flow control. For example, if the power flow is reversed, the inductive loading provided across the source does not provide any useful function.
An object of the present invention is to provide a LLC bidirectional resonant converter with improved forward and reverse power flow control or to at least provide the public with a useful choice.
The present invention aims to overcome, or at least alleviate, some or all of the afore-mentioned problems.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.
The background discussion (including any potential prior art) is not to be taken as an admission of the common general knowledge in the art in any country. Any references discussed state the assertions of the author of those references and not the assertions of the applicant of this application. As such, the applicant reserves the right to challenge the accuracy and relevance of the references discussed.